| Previous Site | Next Site |
Earth Science Conservation Review
| Ardglass | Down |
| Site number: | 568 | ||
| ESCC: | EO | ||
| Locality Type: | Inland exposure | Status: | ASSI |
| Grid Reference: | J325423 Centroid | ||
| Google maps: | 54.31271,-5.96406 | ||
| County: | Down | Council area: | Newry, Mourne & Down District Council |
| Period: | Devonian, Silurian | ||
| Stages: | Lower Devonian | ||
| Lithostrat: | Newry Granodiorite, Newry Igneous Complex | ||
| Site Description | |
|---|---|
| Highlights: | |
Numerous natural exposures occur in the Ardglass area, approximately 3km south of the summit of Slieve Croob. Masses of ultramafic and intermediate rocks of cumulate origin are unique to the north-eastern end of the Newry Igneous Complex. These rocks are collectively referred to as the "ultramafic- intermediate complex" (Meighan and Neeson, 1979). | |
| Introduction: | |
The ultramafic-intermediate complex that occurs at the north-eastern end of the late Caledonian Newry Igneous Complex is well exposed at Ardglass. The site is situated to the northwest of Seeconnell Hill. Site access is via the C class Ardglass Road; vehicles can be parked on grassed road verges adjacent to the area of interest. Landowner permission should be sought before entering the land. The first edition of the Banbridge (Sheet 48) one-inch to the mile geological map (Geological Survey of Ireland, 1871) provides no indication of the existence of an ultramafic - intermediate complex. However, the accompanying geological memoir (Egan, 1872) describes "syenitic granite", a term used for rocks containing "hornblende in great abundance". Reynolds (1934 and 1936) was the first worker to investigate and publish details of the occurrence and petrology of these rocks. This work included produced a lithological map of the distribution of rock types, internal contacts in the ultramafic-intermediate complex, and its relationship to the more extensive granodiorite plutons and surrounding country rock. Since the pioneering work of Reynolds, further research has been carried out on the structure and petrology of the north-eastern end of the Newry Igneous Complex (Grant, 1961; Neeson & Meighan, 1978; Meighan & Neeson, 1979; Neeson, 1984). This later work has led to a better understanding of the magmatic processes which led to the formation of the rocks. The mode of formation of the Newry Igneous Complex, including the ultramafic-intermediate complex, has been the subject of much debate since the early work of Reynolds. The early opinions of Reynolds (1934) and Bailey (1936) favoured a magmatic origin for the rocks. Reynolds (1944) later proposed a non-magmatic 'transformist' origin. Grant (1961) returned to the magmatic model. More recent work (Neeson & Meighan, 1978; Meighan & Neeson 1979), integrating geochemical data with field evidence and petrography supports a magmatic origin for the major rock types. This work also proposed that a process of crystal accumulation from intermediate magma compositions produced the ultramafic rocks and associated meladiorites. The Newry Igneous Complex, including the ultramafic - intermediate complex, is late Caledonian in age (late Silurian to early Devonian). A whole-rock Rb/Sr isotopic age of 399±21Ma was established for granodiorites from the southwest area of the Newry Igneous Complex (O'Connor, 1975). Meighan & Neeson (1979) produced a Rb/Sr age of 403±3Ma for rocks in the ultramafic- intermediate complex at and an age of 399±3Ma for granodiorite from the northeast pluton. Field relations indicate that the ultramafic - intermediate complex represents the first (oldest) major phase of intrusion of the Newry Igneous Complex. The most recently published map which covers this site and shows the position of the ultramafic - intermediate complex is the second edition of the 1:250,000 scale Solid Geology Map of Northern Ireland (Geological Survey of Northern Ireland, 1997). | |
| Description: | |
The site forms part of the ultramafic-intermediate complex of the Newry Igneous Complex. This complex contains rocks ranging from ultramafic to intermediate composition. The main rock types reported include augite-monzonite, augite-biotite-diorite, hypersphene-monzonite and biotite-pyroxenite. Rocks exposed at this site are mainly coarse-grained, biotite-pyroxenites of ultramafic composition and meladiorites of intermediate composition. These two rock types occur in close association. Biotite-pyroxenite can be seen as alternations with, or lenses within, strongly laminated meladiorite. Viewed in thin sections (Meighan, pers. comm. 1999) the main minerals in the biotite-pyroxenite are seen to be biotite, clinopyroxene and apatite, hence the rock is truly ultramafic. The meladiorites are often heterogeneous with variable content of either biotite or clinopyroxene. Also present at this site are light coloured granodiorite sheets and pegmatite veins. The granodiorite sheets have sharp and diffuse contacts with biotite-pyroxenite and meladiorite, indicating a degree of brittle failure during intrusion. Pegmatite veins have a very coarse-grained appearance and are composed mainly of feldspar, quartz and biotite mica. | |
| Importance: | |
The Ardglass site is of national importance offering access to high quality outcrop of the ultramafic - intermediate complex of the Newry Igneous Complex. The ultramafic - intermediate complex is exposed over a relatively restricted area and offers a unique opportunity to study such rock types in Northern Ireland. The rocks are important as they provide evidence in support of a magmatic origin for the ultramafic - intermediate complex and the Newry Igneous Complex in its entirety. Also, some of the rock types found within the ultramafic - intermediate complex are likely to approach parental magma composition. | |
| Interpretation: | |
Field evidence, petrology and geochemistry support the view that ultramafic rocks and associated meladiorites were produced by a process of crystal accumulation (cumulates) from magma of intermediate composition. Some of the rock types found within the ultramafic-intermediate complex are likely to approach the parental magma composition. Field evidence suggests that the rocks of the ultramafic - intermediate complex were emplaced before the main granodiorite bodies to the southwest. | |
| Conclusions: | |
The Ardglass site is of national importance offering access to high quality outcrop in the ultramafic-intermediate complex at the northeast end of the of the Newry Igneous Complex. The site offers rare opportunities to study such rock types in Northern Ireland. The rocks are important as they provide evidence that supports a magmatic origin for the ultramafic - intermediate complex and the Newry Igneous Complex in its entirety. | |
| Notes: | |
For information and references on other sites within the Newry Igneous Complex see the following sites: Key Site 569 - Slieve Croob Key Site 570 - Shannaghan Hill Key Site 571 - Ballymagreehan Quarry Key Site 572 - Rathfriland Key Site 573 - Gransha Key Site 574 - Aughnagon Quarry Key Site 575 - Goraghwood Quarry Key Site 576 - Newry By-pass Key Site 577 - Cam Lough Quarry Key Site 578 - Kearney Point Key Site 579 - Ballyhalbert Pier For general information and references on the Caledonian Igneous Complexes of N. Ireland, and for directions to other regional sites, see the following site: Key Site 595 - Introduction to the Caledonian Igneous Complexes of N. Ireland | |
| Keywords | |
|---|---|
| Rocks: | Granodiorite, Pegmatite, Pyroxenite, Diorite, Monzonite |
| Structures: | Caledonian, pluton |
| Relations: | Intrusion |
| Access | |
|---|---|
| Approach: | Site access is via the C class Ardglass Road. |
| Management: | |
This site is situated in an area of fenced farmland which is currently used for grazing livestock. There is an abundance of outcrop around Ardglass, consequently there is no need to restrict hammering or sampling at this site. The rocks of the Newry Igneous complex are considered to be prospective for a number of minerals including base metals and gold. Licensed mineral exploration and production has previously been carried out in Counties Armagh and Down. The area which includes this site is likely to attract further exploration activity. | |
| Uses | |
| Uses: | Farmland |
| Map(s): | GEOLOGICAL SURVEY OF IRELAND, 1871. 1:63,360 Geological Sheet 48 (Banbridge). (Dublin, Ordnance Survey for Geological Survey of Ireland). GEOLOGICAL SURVEY OF NORTHERN IRELAND, 1997. Northern Ireland. Solid Geology (2nd edition). 1:250,000. (Keyworth, Nottingham: British Geological Survey). | ||
| Record type: | ESCR report | ||
| Entered by: | E M Porter | ||
| Last updated: | 03 MAR 2001 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Ardglass, County Down, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=568. Accessed on 2026-11-04. |
| Previous Site | Next Site |